What is MobX, and what are its core concepts and working principles?

MobX is a state management library based on Functional Reactive Programming (FRP) that makes state management simple and scalable by transparently applying reactive programming paradigms. The core philosophy of MobX is "anything that can be derived from the state should be derived automatically," which means that when state changes, all derived values that depend on that state (such as computed properties, reactions, etc.) will automatically update.

The core concepts of MobX include:

1. Observable: Use observable, observable.object, observable.array, and other methods to create observable state. When these states change, MobX automatically tracks and notifies relevant observers.

2. Computed: Use computed to create derived values that are automatically calculated and cached based on their dependent observable states. They are only recalculated when dependencies change, providing efficient caching mechanisms.

3. Actions: Use action or action.bound to modify state. In MobX 6, all state modifications must be done within actions, which helps track state changes and ensures predictability.

4. Reactions: Include autorun, reaction, and when, used to automatically execute side effects when state changes. autorun executes immediately and re-runs when dependencies change; reaction provides more fine-grained control, allowing you to specify tracking functions and effect functions; when executes once when a condition is met.

5. Observer: Use the observer higher-order component or useObserver hook in React components to make components responsive to state changes and automatically re-render.

MobX works based on a dependency tracking system. When observable objects are accessed, MobX establishes dependency relationships; when observable objects are modified, MobX notifies all derived values and reactions that depend on it, triggering corresponding updates. This mechanism allows MobX to efficiently manage state, avoiding the tedious process of manually triggering updates.

Compared to other state management libraries like Redux, MobX offers advantages such as:

• Less boilerplate code
• More intuitive state management approach
• Automated dependency tracking
• Better performance (through fine-grained updates)
• Easier integration with TypeScript

MobX is suitable for applications of various sizes, especially those that require complex state management and reactive updates.